The present invention relates generally to the field of screen and frame assemblies for windows, doors and the like, and in particular, to screen and frame assemblies in which the screen is secured to the frame by a curing process, and methods of manufacturing such products.
Over the years, many different types of screens have been used to prevent the ingress of insects and other pests into indoor areas, while still providing ventilation. Typical screen assemblies comprise screen cloth, fabric, or mesh attached to a screen frame in a manner that will be discussed in greater detail below. As used herein, the term “screen” includes screen cloth, fabric, mesh, or similar ventilation material.
Screen frames for windows, doors, and the like are commonly made of four elongated frame members, often referred to as screen bars (or screen bar members), of uniform cross section. These bars are typically roll-formed from aluminum or sheet steel, although some may be extruded aluminum. Plastic and wood are also used, but to a lesser extent. These screen bars are supplied from the screen bar manufacturer in lineal form and are cut to a final length by the screen assembly manufacturer. Further, these screen bars are held together at the corners with plastic or metal inserts, called corner keys, to form the screen frame.
Different style corner keys are available and are designed to match the particular screen bar used. The most popular corner key allows the screen bar to be cut straight at 90 degrees at the ends. These keys typically are made from injection molded plastic and have a square block body to visibly fill the corner area of the frame. Attached to the body are insertion prongs that are pushed into the hollow screen bar profile to create friction fit connections. Corner keys requiring a 45 degree miter cut on the ends of the screen bar also can be used. These keys, usually metal, are less expensive and are entirely hidden inside the screen bar. These keys also provide a friction fit connection.
Screen material is typically affixed to the screen frame, in a manner discussed below, to form a screen and frame assembly. These assemblies may then be removably secured to windows, doors (e.g., patio screen doors), operable skylights, and the like. Screen and frame assemblies for such openings are very similar, often differing only in size. Accordingly, for brevity, screen and frame assemblies for windows are described herein. Nevertheless, it will be understood that this discussion applies equally to screen and frame assemblies for doors, operable skylights and virtually any opening provided in a building.
It is generally desirable that the screen be a light weight fabric or mesh, and stretched taut across the screen frame to avoid unsightly sag and to allow a viewer to see through the screen with minimal visual interference. However, if the screen is tensioned excessively, the screen bars deform inwardly in an hourglass shape. This resultant shape is not only aesthetically undesirable, but also can prevent proper installation in the window opening. Excess screen tension also increases the risk of tearing the screen during manufacture of the screen and frame assembly or while the assembly is in service. Typically, the screen is fiberglass yarn or roving, which is coated, for example, with polyvinyl chloride (PVC), woven and heat fused. Another popular form of screen is made by weaving drawn aluminum wire, which is subsequently painted.
Within the industry, it is typically a practice to secure screen material in open grooves formed along inside edges of the screen frames using a stuffer strip known as “spline” and its associated fastening techniques. The open grooves are known as “spline grooves.” A spline is often a wire-like, extruded rigid plastic or foam material, although some splines are made from metal, especially for use with aluminum screens. A spline is usually round or T-shaped in cross section, but can be U-shaped, for example.
A standard procedure for manufacturing and hand wiring a screen and frame assembly is discussed in more detail below. First, the screen bars are cut to length, accounting for the corner key dimensions. Then, the screen frame is assembled using the cut screen bars and corner keys. When light construction screen bars are used, as is often the case, a balance between pre-bow tension and screen tension is necessary to ensure straight screen bars and desirable screen tension in the final assembly. When the screen bar has insufficient pre-bow tension, the bars are deformed by hand a sufficient degree after the corner keys have been inserted. The amount of pre-bow is usually determined based on experience, but is typically a few millimeters of bow per meter length of the screen bar.
The screen frame is then secured to a table using locator (stop) blocks, which prevent shifting and maintain the frame square during screen installation. The table typically has permanent stop blocks for orienting the screen frame. To avoid hourglassing, removable blocks are located on the inside of the frame segment to limit deflection of the screen bar by the screen tension on assembly. More elaborate tables use removable blocks arranged in grooves cut into the table, with the removable blocks being secured by integral friction clamps.
After the screen frame is secured to the table, the screen is pulled from a roll and positioned to cover the opening formed by the frame. Ideally, no excess screen is used, but this is sometimes difficult to achieve in practice. As a result, most manufacturers cut the screen some predetermined length wider than the frame width, so that the screen is pulled past the end of the frame to ensure that sufficient amount of screen can be rolled into the spline groove along the frame perimeter. In either technique, the screen is positioned over, with edges parallel to, the secured screen frame.
The screen and spline are installed into the spline groove by starting in one of the frame corners. The screen is then stretched taut at the next corner with one hand, keeping it straight and parallel to the edge of the mating screen bar. The spline is simultaneously held above the groove in the same manner as the screen, with the same hand. With the other hand, the installation roller is pushed along towards the upcoming corner with a firm downward force to push the spline into and trap the screen in the spline groove. This action is repeated on the second and third screen bars. On the last screen bar, most of the tension is set into the screen. On this leg, the screen is pushed into the screen bar with the installer's finger, just prior to the insertion of the spline. This pre-insertion technique reduces the final tension in the screen to the desired level. The spline is cut at the final corner with a utility knife.
After the spline and screen are inserted in all screen bars, excess screen around the edge of the frame is cut away with a utility knife. To do this, the point of the blade is pushed against the screen bar, through the screen, immediately adjacent to the spline groove around the outside edge of the screen bar. Care must be taken to cut the screen close to the spline groove without cutting the screen covering the opening formed by the frame. The finished screen and frame assembly is removed from the table, inspected, and any necessary hardware is attached.
The current hand wiring process using conventional splines has several drawbacks. For example, most screens and frame assemblies must meet industry standards. These standards cover particular elements of screen and frame assemblies for windows, patio doors and the like. For example, some standards set forth tolerances in terms of the strength of the screen, the strength required to fasten the screen to the screen bar, the amount of sag in the screen, etc. Although these standards generally can be met by using the spline technology discussed above, very close and consistent dimensional tolerances are required between the spline and the spline groove, respectively, in order to achieve the specified fastening strength. These tolerances require close attention and skill with current screen bar roll-forming and extrusion technology and current spline hand wiring techniques. Any out-of-tolerance spline and screen bar produced costs the manufacturer in wasted time, material and goodwill.
Further, the amount of force required by an installer to secure the screen with the spline in the spline groove may be high enough to cause repetitive strain injury (e.g., carpal tunnel syndrome) to one who routinely performs this job. This is of major importance, since this type of injury is serious and has received heightened public awareness. Further, such an injury to an installer is also costly to the manufacturer in terms of compensation and loss of skilled labor.
Also, the hand wiring technique is particularly difficult and time-consuming. Notably, it is difficult to control the wire-like spline material and simultaneously control the screen tension with one hand, while the spline is rolled in with the other hand. This operation requires a high degree of skill and careful attention. This adds to the final manufacturing cost, and, hence, increases the final cost to the consumer. Final product consistency is difficult to maintain.
In addition, quality control is also an issue with current spline techniques. Specifically, installers have learned ways to make their jobs easier, to the detriment of quality control. This is particularly true when using PVC spline. For example, an installer will stretch the PVC spline just prior to insertion, in order to reduce the diameter of the spline. This, of course, makes it easier to install. However, this also reduces the “pull-out” force or attachment strength of the spline and screen. The result is that the screen can be more easily pulled out from the spline groove, which is undesirable.
There are other drawbacks associated with conventional spline techniques. In particular, the use of a separate fastening device, such as a spline, requires separate inventory control and associated costs. Screen manufacturers prefer to minimize inventory. Therefore, it is desirable to eliminate the spline as a separate item. Also, the need to have a strong interference fit in securing the spline necessitates stiff walls on the spline groove. Further, the spline technology makes the design of automatic assembly equipment extremely complex.
Accordingly, there have been some attempts in the art to provide screen and frame assemblies without a traditional spline. Such systems generally require some type of thermoplastic resin or hot melt adhesive. As is often the case, such systems are overly complex and require high manufacturing precision. Further, these techniques can be slow and cumbersome and therefore impractical in the manufacture of screen and frame assemblies for windows and the like. For example, these known systems typically require external tensioning until the thermoplastic resin or hot melt cools and solidifies.
In recent years, numerous modifications to the traditional hot melt adhesive techniques have been developed. For instance, techniques such as light energy methods are now being used to solidify compounds instead of the previously used heat curing system. These new light energy methods, such as the ones used in the current disclosure, are both chemically and practically different than hot melt methods.
Hot melt adhesives can be either curable or non-curable. Non-curable hot melt adhesives are usually formed from derivatives of polyester, polyamide, polyolefin, polypropylene, polyurethane, butyl and ethylene vinyl acetate functional groups. Each of these chemical groups has distinct physical properties thereby making some better hot melt adhesive candidates than others. For example, polyester and polyamide adhesives are oftentimes preferred over others. In general, the hot melt technique uses heat to adhere objects together. Once the resin is heated and applied, the system must be cooled for complete adhesion to occur. The adhesive is normally liquid upon application and later sets to form a solid bond. The regular hot melt adhesive (non-curable) can be applied, dried, and then later re-melted during the adhesion process.
In general, curable hot melt adhesives are similar to non-curable adhesives. One difference, however, is that adhesion must occur immediately after application for curable hot melt adhesives. Because attachment must occur directly after application of the hot melt, this technique is usually not used. Hot melt adhesives are often more practical. As with non-curable adhesives, heat is used to set the compound and establish the bond.
One approach that may be used instead of the hot melt process is ultraviolet curing. For this method, ultraviolet light, instead of heat, may be applied to acrylate and methacrylate containing resins in order to attach the elements. The resins may contain a special additive known as a photo-initiator that responds to the ultraviolet light and crosslinks the polymer resin. These functional groups are chemically different than the above mentioned compounds. The pure acrylates do not contain nitrogen and therefore cannot be defined as either polyamides or polyurethanes, further differentiating them from the hot melt technology. Accordingly, the final resins of ultraviolet curing are chemically different from the final resins of hot melt curing because of additions like those described above that are made to the resins.
As an example, Loxeal srI (MI) Italy produces an ultraviolet curable compound under the trade name Loxeal Anerobic 3025 that includes a photo-initiating element to facilitate the bonding reaction. When light of the correct wavelength is applied to the resin, it causes some of the carbon-carbon double bonds to break into radicals (chemical species with and odd number of electrons), which then react with acrylate or methacryate compounds in a free-radical reaction to cure the resin. In addition, there is a coordination that can be made between the emitted wavelength of light and the compound formulation to create different characteristics of curing.
It is also possible to have the compounds break into ions instead of radicals when the light is applied. This is called the cationic reaction type. In this type of situation, the bonds break so that a full electron pair is transferred from one half of the molecule to another so that there is an even number of electrons and either a net positive or negative charge. In contrast, hot melts do not add photo-initiators and do not use light. Instead, hot melts use heat to complete the adhesion process. Further, hot melt manufacturers often add sufficient amounts of carbon black to the adhesive in attempt to block out any ultraviolet rays. In addition, light absorbing and stabilizing compounds are sometimes added to prevent a reaction between the adhesive and ultraviolet light. Thus, ultraviolet curable compounds have not been used heretofore to attach screens to screen frame assemblies.
Accordingly, there exists a need for a screen and frame assembly that eliminates the requirement of a separate, mechanical spline. In addition, there exists a need to manufacture screen products more easily, where a screen may be secured to a frame quickly, with reduced manual labor. Further, there exists a need for a screen and frame assembly that substantially reduces the level of skill and time, as well as physical force, required to attach screen to a screen bar and/or frame.